Algicidal post treated roofing granules

ABSTRACT

Algicidal properties are imparted to conventional color coated roofing granules by incorporating metallic algicides with the processing oil conventionally employed in the postreatment of such color coated roofing granules. The metallic algicides employed have a particle size not exceeding about 100 mesh, preferably less than about 200 mesh, and more particularly having a particle size not exceeding about 325 mesh. A variety of metallic algicidal compounds can be employed, with copper algicides being particularly advantageous. The processing oil, having a viscosity of about 100-500 SUS measured at 100*F and present in an amount generally of about one-fourth gallon to about 1 1/2 gallons per ton of base granules, forms a thin film on the surface of the coated granules, with a portion of said oil generally being absorbed into the color coating and possibly into the base granules and into the asphalt saturated base sheet upon application thereto. The metallic algicides adhere to the surface of the granule color coating, with the finer particles thereof being adsorbed into the color coat with the processing oil. By employing a mixture of copper and zinc algicides, a bimetallic toxic effect particularly effective in retarding the growth of algae and/or fungi is achieved.

United States Patent 1 Horai, Jr. et a1.

1 1 ALGICIDAL POST TREATED ROOFING GRANULES [75] Inventors: John C.Horai, Jr.; David C. Little,

both of Hagerstown, Md.

[73] Assignee: GAF Corporation, New York, NY.

[22] Filed: Oct. 25, 1972 [21] Appl. No.: 300,864

[52] US. Cl. 106/15 AF [51] Int. Cl C09k 3/00 [58] Field of Search117/100 D, 27, 70 S, 87, 117/88, 30, 32,140 A; 106/15 AF [56] ReferencesCited UNITED STATES PATENTS 1,970,471 8/1934 Nichols n 117/27 2,003,8496/1935 Alton 1 17/100 D X 2,078,359 4/1937 Young ll7/l00 D X 2,362,489l1/l944 Jewell 117/100 D 2,614,051 10/1952 Buzzell et all 117/273,208,871 9/1965 Langseth et al 117/27 3,255,031 6/1966 Lodge et a1.117/27 3,476,577 ll/1969 Davie t W 106/15 AF 3,494,727 2/1970Rapaportn... 106/15 AF 3,507,676 4/1970 McMahon r r 117/25 X 3,528,8429/1970 Skadulis 1 17/100 S X 3,598,627 8/1971 Klimboff 106/15 AF FOREIGNPATENTS OR APPLICATIONS 491,238 2/1947 Canada 106/15 AF 1 June 10, 1975Primary Examiner-William D. Martin Assistant ExaminerDennis C. KonopackiAttorney, Agent, or FirmWalter C. Kehm; Joshua J. Ward [57} ABSTRACTAlgicidal properties are imparted to conventional color coated roofinggranules by incorporating metallic algicides with the processing oilconventionally employed in the postreatment of such color coated roofinggranules. The metallic algicides employed have a particle size notexceeding about 100 mesh, preferably less than about 200 mesh, and moreparticularly having a particle size not exceeding about 325 mesh. Avariety of metallic algicidal compounds can be employed, with copperalgicides being particularly advantageous. The processing oil, having aviscosity of about 100-500 SUS measured at 100"F and present in anamount generally of about one-fourth gallon to about 1% gallons per tonof base granules, forms a thin film on the surface of the coatedgranules, with a portion of said oil generally being absorbed into thecolor coating and possibly into the base granules and into the asphaltsaturated base sheet upon application thereto. The metallic algicidesadhere to the surface of the granule color coating, with the finerparticles thereof being adsorbed into the color coat with the processingoil. By employing a mixture of copper and zinc algicides, a bimetallictoxic effect particularly effcctive in retarding the growth of algaeand/or fungi is achieved 30 Claims, No Drawings ALGICIDAL POST TREATEDROOFING GRANULES BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates to roofing granules having algicidal properties.More particularly, it relates to a simplified method for producing novelcolor coated roofing granules possessing algicidal properties foreffectively retarding the biological growth of algae and/or fungi onroofing surfaces.

2. Description of the Prior Art Roofing granules, both natural andartificially colorcoated granules, are extensively used in roll roofingand asphalt shingle compositions. The roofing granules are generallyembedded in the asphalt coating on the surface of an asphalt-impregnatedfelt base material, the granules thus forming a coating that provides anadherent, weather-resistant exterior roofing surface. As this outergranule coating also provides the esthetic effect observable withrespect to the roofing composition, the appearance of the granules is ofmajor marketing interest. For this reason, therefore, a pigmented colorcoat is ordinarily applied to the base mineral granules to enhance theirvisual, decorative effect.

As white or light-colored roofs are particularly favored in warmerclimates, TiO pigment is commonly used in the production of lightcolor-coated roofing granules. In such warmer climates, as in thesouthern part of the United States, discoloration of asphalt roofingcompositions by the growth of algae and/or fungi is particularlynoticeable on the white or light-comic? roofs otherwise so desired andpopular in such regioiis Upon discoloration, the roof becomes unsig lyin appearance and is found to cause a greater he absorbence as, forexample, when a white roof is turned dark brown or black in a period ofa few years in use.

Nor is this problem, so widespread in areas such as the southern UnitedStates, particularly the gulf state area, confined necessarily to suchregions. Thus, discoloration of roofing surfaces by the growth of algaeandlor fungi has also been found in the northern part of the UnitedStates, particularly so in areas along rivers and lakes and along thenorthern coastal regions. While home owners and others have been awareof this discoloration problem for many years, effective, practicalsolutions thereto have not been forthcoming at a reasonable cost. Theproblem of roofing granule discoloration, therefore, has remained amajor marketing problem for the roofing industry.

For many years, this problem of roofing granule discoloration wasbelieved to be caused only by fungi, as is the case with respect to someoutdoor paint surfaces. Many different types of fungi have, in fact,been isolated from discolored roofing surfaces. More recently, however,it has been learned that other organisms contribute principally to thisdiscoloration and have been identified as terrestrial blue-green algaeof the Cyanophyta division. Such algae are transferred through the airas spores and/or vegetative matter and deposited on roofing surfaceswhere they thrive and grow. Natural pigments produced by the algae addto the dark discoloration of the roof, which is generally firstnoticeable in spots that develop into dark vertical streaks thatgradually darken until the entire roof becomes a totally discoloredblack within five to fifteen years. Predominant algae thus identifiedfrom infested roofing shingles include Gloeocapsa Magma, TolypothrixByssoidea, Nostoc sp. and Scytonema sp. ln general, metallic algicidesthat are effective in retarding the biological growth of such algae arelikewise effective in similarly retarding the growth of fungi. Theincorporation of a metallic algicide in the color coat of roofinggranules, therefore, has heretofore been proposed in order to inhibit orprevent the discoloration of roofing surfaces containing such granulesas a result of algae and/or fungi growth.

' The incorporation of a metallic copper algicide in the color coat ofroofing granules was disclosed in the Skadulis patent, US. Pat. No.3,528,842. Skadulis particularly proposes the incorporation of copperalgicides that are substantially water-insoluble but that have limitedsolubility in acidic solutions, e.g. Cu O. Highly water-soluble copperalgicides, such as CuSO were indicated as being ineffective for thisapplication since it was suggested that such algicides would be leachedout of the color coat very rapidly, i.e. within a few months, so thatthe resistance to algae growth and roofing discoloration would not beeffective over any reasonable length of time. Skadulis also indicatedthat virtually water-insoluble compounds, such as CuO, would not beeffective because, it was suggested, of insufficient solubility thereofin rainwater and dew (Column 2, lines 24-44). Similarly, slightlysoluble zinc algicides were disclosed for incorporation in the colorcoat of roofing granules in the McMahon patent, US. Pat. No. 3,585]: 76.As was pointed out in the McMahon patent in (55 n 2, lines 58-65, suchzinc algicides are effective when employed in an amount constituting atleast about 1% by weight of the base mineral grnaules, i.e. about 20lbs. of the zinc algicide compound or metal per ton of granules.

The incorporation of particular copper or zinc algicides in the colorcoat of roofing granules, in the manner and in the quantities taught bythe Skadulis and McMahon patents, imparts a desirable resistance ofroofing surfaces containing such granules to discoloration upon exposureto atmospheric weathering. The teachings of these patents, however, havenot led to the development, commercial availability and use of algicidalroofing granules providing the desired degree of algae and/or fungiresistance over an extended period of time at economically competitivecost. In part, of course, this unavailability of a totally satisfactoryalgicidal roofing granule reflects the continual desire in the roofingindustry for a more effective algicidal effect from a roofing granule ofever diminishing incremental cost to achieve such an algicidal effect.Any incorporation of metallic algicides in an otherwise conventionalroofing granule coating in order to achieve the necesary or desirablealgicidal effect necessarily adds an incremental cost to the roofinggranule and to the roofing material incorporating such an algicidalgranule. While the desired toxic effect is a necessary or highlydesirable feature of the algicidal roofing granule, the providing ofthis property or function is an expense item that, from a marketingviewpoint, must be minimized to the fullest possible extent. The use ofminimum quantities of metallic algicides to produce a desired level ofeffectiveness over an extended period of time is, therefore, highlydesirable. While the prior techniques have imparted an algicidal effectto roofing granules, an enhanced effect would provide further assuranceof the desired toxic effect, thereby enhancing the quality of suchgranules. In this regard, it should be noted that the algicidal granulesof McMahon require the incorporation of a relatively large amount ofzinc for effective algicidal action as noted above. As the amount ofmetallic algicide required for effective action increases, the cost ofthe resulting algicidal granule is directly increased thereby. Inaddition, the use of relatively large amounts of metallic algicidesfrequently requires the incorporation of pigment in the granule coatingin amounts in excess of that otherwise required to achieve a desiredroofing granule color. As the amount of Cu O employed is increased, forexample, the amount of TiO pigment that must be employed in the granulecoating composition to produce a white roofing granule is also generallyincreased. Such an additional requirement necessarily adds to theoverall cost of the algicidal roofing granule product and of roofingmaterials made therefrom.

The requirements flowing from the assumptions and teachings of the priorart tend to limit or restrict the metallic algicidal materials to beemployed in a manner not necessarily consistent with the economicavailability and feasibility of such mateials in any particularapplication. Optimum flexibility as to the metallic algicides employedis, in other words, another desirable aspect for the providing of aneconomically attractive a1 gicidal roofing granule to the roofingindustry. One further troublesome aspect of previous efforts to impartalgicidal properties to roofing granules has been the practicalnecessity for producing such algicidal roofing granules as a separateproduction operation apart from the production of conventional,non-algicidal, colorcoated roofing granules because of the variation inthe color coating formulation necessarily required to incorporate thealgicidal compound into the color coating. As the vast preponderance ofroofing granules presently manufactured are of conventional,non-algicidal character, the interruption of such conventional roofinggranule production and the scheduling and inventory problems associatedtherewith all tend to create a further economic disadvantage associatedwith the production and marketing of algicidal roofing granules. Ashereinabove indicated, the commercial acceptance and use of algicidalroofing granules depend upon the providing of an economically acceptablebalance between algicidal effectiveness and the incremental costrequired to achieve such algicidal properties as compared with the costof conventional roofing granules, all taken in light of the degree ofalgicidal effectiveness achieved. In light of these factors, therequirements for the production of algicidal roofing granules inaccordance with the teachings of the prior art constitute a furtherdetrimental element serving to diminish the prospects for employingalgicidal roofing granules despite the genuine need for algicidalcontrol and an improved resistance of roofing surfaces to discolorationduring extended periods of exposure to atmospheric weathering.

It is an object of the present invention, therefore, to provide improvedalgicidal roofing granules.

It is another object of the invention to provide an improved process forthe production of such algicidal roofing granules.

It is another object of the invention to provide algicidal roofinggranules having effective algicidal properties at economicallyacceptable levels of metallic algicide content.

It is another object of the invention to provide a process for theproduction of roofing granules having enhanced flexibility andcompatibility with respect to the conventional production of colorcoated roofing granules.

It is a further object of the invention to provide roofing surfaceshaving an enhanced resistance to discoloration during extended periodsof exposure to atmospheric weathering.

With these and other objects in mind, the present invention ishereinafter set forth in detail, the novel features thereof beingparticularly pointed out in the appended claims.

SUMMARY OF THE INVENTION Color coated roofing granules capable ofinhibiting or preventing the growth of discoloring algae and/or fungiorganisms upon exposure of roofing surfaces containing such granules toatmospheric weathering have a conventional color coating on the basemineral granules, with a conventional processing oil forming a thin filmon the surface of the coated granules and metallic algicides in the oilfilm and adhering to the surface of the granule coating by electrostaticand/or mechanical adhesive forces. The metallic algicides are applied toconventionally color coated granules by incorporation with theprocessing oil that is mixed with the color coated granules in anotherwise conventional posttreatment operation. The metallic algicideswill have a particle size not exceeding about lOO mesh, with theparticle size thereof being preferably less than about 200 mesh, orpreferably with the major proportion or substantially all of themetallic algicides having a particle size of less than 325 mesh. Aportion of the processing oil applied to the color coated granules maybe absorbed into the color coating and into the base mineral granulesthemselves. The finer sized particles of metallic algicides employed mayalso be adsorbed into the granule color coating.

Upon incorporation of the algicidal roofing granules of the presentinvention into asphaltic roofing compositions and exposure toatmospheric weathering, the processing oil will weather away anddecompose as in conventional roofing granule applications. The metallicalgicides, however, are substantially retained on the surface of theroofing granules and are not dislodged or loosened therefrom as theprocessing oil weathers away. During periods of rain and dew, themetallic algicides are ionized to form metallic algicidal ions. Thesemetallic algicidal ions are slowly released from the surface of theroofing granules and are leached over the roofing surface, providing atoxic effect that retards or prohibits the biological growth of algaeand/or fungi. This slow release of algicidal ions is found to operateover extended periods of time, even upon exposure under severeconditions of atmospheric weathering, thus enhancing the resistance ofthe roofing surfaces containing such granules to algae and/or fungi overthe reasonable life of the roofing surface.

The production of the roofing granules of the invention does notnecessitate any disruption of conventional production of color coatedroofing granules. The metallic algicides employed can readily beincorporated with the processing oil or eliminated therefrom during theusual post-treatment operation, thereby minimizing the processingoperations, scheduling problems, and handling costs heretoforeassociated with the production of an algicidal roofing granule. Highlydesirable production flexibility is thus achieved. In addition, a widevariety of metallic algicidal compounds can be employed, includingconvenient copper algicidal compounds not heretofore deemed acceptablefor application in algicidal roofing granules. By the incorporation ofboth copper and zinc algicidal compounds in economically suitableamounts, a bimetallic toxic effect can be achieved so as to enhance theretarding or preventing of the biological growth of algae and/or fungi,thus enhancing the resistance of roofing surfaces to algae and/or fungidiscoloration during extended periods of exposure to atmosphericweathering. The present invention, therefore, provides a highlycommercially desirable algicidal roofing granule, combining effectiveinhibition of the biological growth of algae and- /or. fungi withminimum incremental cost and processing requirements to achieve thedesired algicidal properties.

DETAILED DESCRIPTION OF THE INVENTION In the practice of the presentinvention, highly desirable algicidal properties are imparted to colorcoated roofing granules in a convenient, economical and highly effectivemanner. Roofing surfaces containing the novel algicidal granules of theinvention release algicidal ions slowly over an extended period of timeduring periods of rain upon exposure to atmospheric weathering. Theroofing surface is thereby rendered resistant to unsightly discolorationdue to infestation and growth of algae and/or fungi. This highlydesirable feature is accomplished at economically acceptable algicidalcontent levels and overall roofing granule cost, with minimum departurefrom conventional roofing granule production operations. The algicidalproperties of the roofing granules of the invention are effective overextended periods of time and are particularly suitable in humidenvironments normally conducive to the growth of algae and/or fungi.Highly desirable flexibility as to the particular algicidal compoundsemployed also pertains. The toxic effect of the slow release ofalgicidal ions from the roofing granules of the invention is enhanced byemploying both copper and zinc algicidal compounds in the preparation ofthe subject roofing granules. Upon exposure of roofing surfacescontaining such a combination of algicidal compounds to rain and dew,both copper and zinc ions are thereupon slowly leached from the surfaceof the roofing granules and produce a bimetallic toxic effect that isparticularly effective in inhibiting or retarding the biological growthof algae and/or fungi.

The algicidal roofing granules of the present invention are prepared bythe post-treatment of conventional color coated roofing granules. Aswith conventional roofing granules, therefore, any suitable base rawmineral granules, such as greenstone or netheline syenite may be used.In conventional production of artificially colored roofing granules, analkali metal silicateclay coating is applied to the base mineralgranulels and fired to produce a moisture permeable, substantially waterinsoluble, durable, pigmented coating on the base mineral granules. Twogeneral methods are commonly employed for color coating such basemineral granules, both of which can be employed in the practice of thepresent invention. In one such method, re-

ferred to as the continuous paint slurry process, crushed and screengraded mineral granules are constantly mixed with a paint slurrycontaining pigments, clay and sodium silicate in suitable mixingequipment. The thus color-coated granules are then heated to atemperature that may range from about 600F to about l200"F in arotary-type kiln. Dehydration of the silicate occurs, and an extremelyhard color-coated granule is obtained. In the event that the granulesare fired at lower temperatures, e.g. about 500F, the silicate-claycoating may require treatment by the addition of a pickling agent, suchas AlCl solution, in order to properly insolubilize the coating. Uponcooling, the color coated granules are generally post treated withprocessing oil and/or coating compositions as is known in the art.

In another batch-type process, essentially the same coating, firing andpost treatment operations are performed except that a weighed amount ofcrushed and screen graded base mineral granules is mixed with a weighedamount of pigments and clay, and the silicate is added to this premix ina suitable mixer, commonly a tumbling barrel-type mixer. The firing andpost treatment of the color coated granules are as referred to abovewith respect to the continuous process. It is, of course, within thescope of the present invention to provide the color coating on the basemineral granules by any desirable modification of these techniques, orby any other conventional color coating operation. It will also beunderstood that the present invention for imparting algicidal propertiesto conventional color coated roofing granules during the post-treatmentthereof can be employed regardless of the number of such color coatingsapplied to the base mineral granules.

Following the post-treatment operation in which algicidal properties areimparted to the roofing granules as herein provided, the resulting novelalgicidal roofing granules are incorporated in otherwise conventionalasphaltic roofing compositions, such as roofing shingles, rolledroofing, and the like. Such roofing compositions typically have anorganic asphalt-saturated felt base that is coated with an asphalt of ahigher softening point and surfaced with color coated roofing granules,such as conventional non-algicidal roofing granules or, in the practiceof the present invention, the novel algicidal roofing granules hereinprovided. The felt layer is customarily composed of wood fibers, eitheralone or in combination with paper pulp, repulped paper and/or rags,asbestos fibers, or the like. Such felts are generally referred to inthe industry as roofing felts. The saturants most commonly employed tosaturate the felt layer include residual oil, soft residual asphalt andsoft blown petroleum asphalt, and mixtures thereof. Preferred saturantsgenerally have a ring and ball softening point of approximately F tol30F and a penetration of approximately 60 at 77F.

This saturated felt layer is then coated with an asphalt of a highersoftening point and lower penetration than that of the saturant.Preferred materials will generally have a ring and ball softening pointof approximately F to 260F and a penetration of approximately 10 to 50at 77F. Coating asphalts of this type include native and sludgeasphalts, fatty acid pitches and the like. In accordance with customarypractices in the art, this asphalt coating layer is frequently embeddedwith powdered or fibrous fillers of inorganic or organic origin, such aspowdered silica (sand), limestone, slate dust, clay, etc., and mixturesthereof. Upon application of the asphalt coating to the saturated feltlayer, the color coated roofing granules post treated in accordance withthe present invention to impart algicidal properties thereto are appliedto the asphalt layer surface, and the resulting roofing surface is thenpassed through suitable rollers and presses, quenched and otherwisetreated and handled in accordance with conventional practice in theroofing industry. It will be appreciated that numerous variations in theproduction of the desired roofing compositions and in the additivematerials employed are well known in the art and can be employed withinthe scope of the present invention.

In the conventional production of non-algicidal roofing granules, thecoated and fired granules having a hard, durable, tight, weatherresistant, water insolubil ized color coating is post treated by mixingwith a suitable treatment oil, commonly a conventional processing oilalone or in combination with other conventional coating compositions,such as a silicone coater. This post treatment with processing oilprovides useful properties that facilitate the storage, handling and useof the roofing granules and their subsequent effectiveness in asphalticroofing compositions. Thus, post treating the roofing granules serves tolubricate the granules, improving their flow characteristics andhandling properties during passage from the production area intotransport cars, from such cars into storage bin, and the like. Thelubrication of the roofing granules also minimizes undesired attritionof the color coating during transport and other handling, therebylikewise minimizing the formation of undesired dust during suchtransport, storage and handling. Post treatment of the color coatedroofing granules with processing oil also has been found to promote thedesired adhesion of the roofing granules to the roofing felt byproviding a better bonding between the asphaltic coating thereof and theroofing granules. in addition, the processing oil also tends to retardany tendency of the color coating to blister, such blistering beingundesired as it reduces the weather resistant characteristics of thegranules during extended exposure of the granules to atmosphericweathering when employed in such roofing compositions.

The advantages achieved by the post tretment of conventional,non-algicidal roofing granules with processing oils and/or other coatingcompositions are likewise achieved by the post treatment of roofinggranules in accordance with the present invention. The mixing ofmetallic algicidal compounds with the roofing granules and posttreatment processing oil and the resultant adherence of such metallicalgicidal compounds to the surface of the roofing granules, as hereinprovided, imparts highly desirable algicidal properties to the roofinggranules without, in any way, diminishing the benefits otherwiseachieved in conventional post treatment of roofing granules. Theprocessing oil employed in the post-treatment operation of the presentinvention can thus be any of the conventional processing oils commonlyavailable in the art and suitable in conventional post treatment ofroofing granules. Such processing oils are typically petroleum oils ofthree general types, namely (1) paraffin oils, (2) naphthenic oils and(3) aromatic oils or mixtures thereof. Processing oils characterized byhaving a predominant number of paraffin chain carbons, i.e. 55% Cp ormore, are generally considered as paraffin oils. Naphthenic oils areprocessing oils generally characterized by having a large number ofnaphthene ring carbons, i.e. 35% or more Cn. Aromatic oils, on the otherhand, are generally processing oils having a large number of aromaticring carbons, i.e. 35% Ca or more. It will be understood that theconventional processing oils employed may properly be characterized by acombination of such properties, as in an aromatic-paraffinic oil. Suchconventional processng oils generally have a viscosity within the rangeof from about 100 to about 500 SUS at 100F. While lighter oils having aviscosity of from about 100 to about 300 SUS at 100F can be employed,oils having a viscosity of generally from about 300 to about 500 SUS atsaid 100F in that such oils have adequate processing characteristics andtend to facilitate the adherence of the algicidal compounds to thesurface of the roofing granules. In addition, such somewhat heavier oilsare weathered away at a slower rate, so as to extend the period of timeduring which the processing oil is effective in enhancing the overallproperties of the roofing granules during use in roofing compositions.Heavier oils, having viscosities up to about 950 SUS, can also beemployed, such heavier oils enhancing the adherence of the algicides tothe granules, thereby minimizing undesired wash-off of such algicides.Representative illustrative examples of suitable processing oils areTexaco 659 process oil having a viscosity of 300 SUS at 100F and aClay/Gel analysis of 83.3% saturants, 16.1% aromatics and 0.6% polarcompounds; Coray 50 (1507) Granule oil manufactured by Humble oilrefining Company, having a viscosity of 304 SUS at 100F, an anilinepoint of 183.7, and a refractors index at 20C of 1.5007; Sunthene 310process oil manufactured by Sun Oil Company, having a viscosity of 1 l0SUS at 100F and a Clay/Gel molecular-type analysis of 29 wt. aromatics,wt. saturants, and 1.0 wt. polar compounds. It will be appreciated,however, that numerous other commercially available processing oils canbe used in the practice of the present invention.

The processing oils employed in the post-treatment operation of thepresent invention are generally employed in an amount within the rangeof from about one-fourth gallon to about 1% gallons per ton of basemineral granules employed. At lesser amounts, sufficient oil for propercoating of the granules may not be available, and as the amount ofprocessing oil is increased beyond the upper level generally indicated,the additional oil is not required for effective results and a tendencyfor blistering the asphaltic coating of the roofing composition in whichthe granules are employed is introduced. In general, entirelysatisfactory results can be obtained by employing the processing oil inan amount within the range of from about one-half gallon to aboutthree-fourths gallon per ton of base mineral granules employed. It willbe understood that other conventional coating compositions, such as aconventional silicone coater composition, can also be employed in thepost-treatment operation of the present invention to enhance theadherence of the metallic algicides to the roofing granules and for suchadditional purposes that such known coating compositions mightoptionally be employed in the conventional post treatment ofnon-algicidal roofing granules. Reactive silicone monomers such asmethyltriethoxysilane or methyltrimethoxysilane, capable of polymerizingupon contact with moisture, can be dissolved to a desired concentration,eg of about 10 to l% by weight, in methanol, ethanol, trichloroethane orother suitable solvents. A silane composition of from about to l00% byweight solution of methyltriethoxysilane containing about two-thirdsmonomer and one-third polymer by weight in the same solvent is otherillustrative silicone coating composition that can be used with theprocessing oil in the practice of the present invention. Anothersuitable silicone monomer is methyltrichlorosilane applied either in its100% concentrated form or in solution in toluene, benzene, ethyl acetateor any other suitable solvent at any appropriate concentration, e.g.about 10-30% by weight of solution. Such silicone additives may beadvantageously employed in amounts generally from about 1% to about 25%by weight based on the total weight of the processing oil compositionemployed in the post-treatment operation of the invention. Thepost-treatment oil containing such silicone or other conventionaladditives provides the benefits herein indicated for which granule posttreatment is ordinarily employed, and acts as a carrier for thealgicidal material incorporated in the post-treatment operation inaccordance with the teachings of the invention. When employed, theconventional silicon coater additive serves to enhance the adherence ofthe algicidal particles to the surface of the color coated granules.

The conventional processing oil, alone or with other desired components,is mixed with natural or colorcoated roofing granules in a suitablemixing device, eg a rotary mixer, for a sufficient period of time toassure adequate contact of the processing oil composition with theroofing granules being post treated. The amount of time required forthis purpose will, of course, be determined by the operating parametersof any particular application, but in any event is accomplished in arapid, expedient manner. In particular applications, for example,processing oil has been fed to a rotary mixer at the rate of about lbs.per hour, with a 2 minute mixing time being sufficient for adequatecoverage of the roofing granules mixed therewith in the proportionsgenerally indicated above.

In the conventional post treatment of roofing granules and in themodified post treatment operation of the present invention, theprocessing oil forms a thin film on the surface of the color coatedroofing granules. In addition, a portion of the processing oil isabsorbed into the color coating on the base mineral granules. A portionof the processing oil may also be absorbed into the base mineralgranules and the asphalt saturated base sheet. The processing oilforming the thin film on the surface of the granules and that absorbedinto the color coating, the base mineral granules and the asphalt basesheet eventually weather away and decompose upon exposure to atmosphericweathering over a period of time likely ranging from about a half yearto about two-three years. This weathering and decomposition of the posttreatment processing oil occurs with respect to the aligicidal roofinggranules of the present invention in the same manner as with respect toconventional roofing granules. It has been unexpectedly determined,however, that this weathering away of the post treatment processing oildoes not result in any appreciable tendency of the algicidal compoundson the surface of the roofing granules to erode mechanically uponexposure to wind and rain as would heretofore be expected. To thecontrary, the metallic algicidal materials of the present invention arefound to adhere to the roofing granules in a manner not adverselyaffected by the weathering away of the processing oil with which it wasoriginally mixed so as to continue serving as effective algicidalmaterials long after the processing oil has weathered away. It is thisability of the algicidal materials to effectively operate over extendedperiods of time upon atmospheric exposure that serves as the basis forthe novel process of the present invention and the novel algicidalroofing granules obtained thereby.

In the production of the algicidal roofing granules of the presentinvention, the metallic algicidal materials employed are mixed wth thecolor coated roofing granules and with the conventional processing oilcomposition in any convenient mixing device suitable in conventionalpost-treatment operations. If desired, the metallic algicides can bepremixed with the processing oil before mixing thereof with the coatedroofing granules. It should also be noted that, in accordance withconventional practice, the processing oil can be heated in order toenhance the flow characteristics thereof, thus assuring adequate contactand coverage of the processing oil with the color coated granules uponmixing therewith in the granule post-treatment operation. The processingoil is commonly heated to a temperature of from about F to about 250Ffor this purpose.

The imparting of algicidal properties to roofing granules in accordancewith the practice of the present invention can be seen to harmonizeadvantageously with the conventional production of artificially coloredroofing granules and the conventional post-treatment thereof. Nodisruption of the color coating operations is required, and the simpleaddition of metallic algicidal materials in the granule-processing oilmixing action of the post-treatment operation requires a minimaladjustment of ordinary, conventional operations. The present inventionalso permits, in a convenient manner, the production flexibility ofproducing either conventional color coated roofing granules or thealgicidal roofing granules of the present invention as required to meetmarketing requirements. The present invention also provides a highdegree of flexibility with respect to the metallic algicidal material ormaterials employed to impart the desired algicidal properties to theroofing granules. The metallic algicidal compounds thus employed may beany of the available metallic materials generally known as possessingalgicidal properties and that, when employed in the roofing granules ofthe present invention, release algicidal ions slowly during periods ofrain and dew. The release of such algicidal ions and the leachingthereof over the roofing surface produces the desired effect ofprohibiting or retarding the biological growth of algae and/or fungi onthe roofing surface. It should be noted that known metallic algicidalmaterials that are either slightly soluble or very soluble in water canbe employed, including such materials not heretofore deemed suitable foruse in algicidal roofing granules as hereinabove noted. While metallicalgicidal ma terials that are very soluble in water will generally beleached from the roofing granules of the invention at a more rapid ratethan those having a more limited solubility in water, algicidalmaterials of both types can be employed in the present invention andwill be found to provide the desired leaching of algicidally effectiveions over extended periods of time upon atmospheric exposure whenincorporated in roofing compositions. In this regard, it has been foundthat the fundamental and essential feature effecting the algicidalaction achieved is the ionization of the metallic algicidal materials soas to release metallic algicidal ions for leaching over the roofingsurface. A metallic algicidal compound having a limited solubility inwater is found, upon exposure to moisture during periods of rain anddew, to become ionized and release metallic algicidal ions having atoxic effect on the biological growth of algae and/or fungi. Suchalgicidal materials are effective over very extended periods of timebecause of the slow rate at which metallic algicidal ions are releasedfrom the algicidal materials adhering to the surface of the roofinggranules. When a more highly water soluble material is employed, it hasbeen found that a somewhat more rapid rate of metallic algicidal ionleaching takes place. but not at such a rapid rate as to deplete theavailable supply of metallic ions over an unacceptably short duration oftime. In this regard, one factor believed pertinent to the effectivenessof more highly water soluble algicidal materials over extended periodsof time is the possible leaching of metallic ions from the surface ofthe granule color coating into the interstices of the coating itselfduring periods of heavy rain. During such periods of heavy rain,therefore, a wash-out effect leaching ions effectively over the surfaceof the roof for effective algicidal control is likely accomplished by acorresponding release and leaching of metallic algicidal ions into thecolor coating of the roofing granule itself. Thus, a reservoir supply ofmetallic algicidal ions is thus created in the granule color coating,effectively extending the period of time which such algicidal ions arereleased and leached for effective algicidal control. Algicidal ionsleached into the color coating will be released, of course, uponcontinued exposure to moisture passing into the moisture permeable colorcoating during periods of rain and dew during continued exposure toatmospheric weathering. As will be appreciated from the above, it isalso desirable in the practice of the present invention to employ acombination of highly soluble algicidal materials and those of lesserwater solubility so as to assure the desirable wash-out release ofalgicidal ions over the surface of the roof and the slow release ofalgicidal ions over extended periods of time during the effectivealgicidal life of the subject roofing granules.

The algicidal materials used herein slowly release toxic ions thatinhibit or prevent unsightly discoloration of roofing surfaces due tobiological growth. As indicated above, such discoloration is nowbelieved to be caused principally by various algae, although fungispores are also found to exist on roofing surfaces susceptible tobiological growth. As a result, some confusion or imprecision haspersisted in general discussions of roofing discoloration, with suchdiscoloration sometimes being casually referred to as fungidiscoloration even though the biological growth of algae may actually bethe major contributing factor therein. For this reason. therefore, thepresent invention is disclosed and claimed herein with respect to theinhibition or retardation of the biological growth of algae and/orfungi. It will be understood that the slow release of toxic ions fromthe algicidal roofing granules of the invention is effective, in anyevent, in inhibiting or preventing the unsightly discoloration ofroofing surfaces due to biological growth discoloration of roofing surfaces due to biological growth regardless of the generalcharacterization of such undesired growth as algae or fungi growth inordinary consideration of roofing performance with respect to resistanceto discoloration due to biological growth. Suitable compounds having thedesired algicidal properties will sometimes be suitable also for fungicontrol purposes.

Among the suitable metallic algicidal materials that can be employed inthe practice of the present invention are cadmium algicides, nickelalgicides, silver algicides, copper algicides and zinc algicides. Themost convenient and economically suitable metallic algicidal materialsare the copper and zinc algicides generally known in the art. Nickel orsilver-containing compounds, such as the metal or oxide, are generallynot particularly advantageous from an economic viewpoint.Cadmium-containing compounds, e.g. cadmium metal or oxide, are notgenerally desirable from a toxicity viewpoint. Among the wide range ofknown copper algicidal compounds that can be employed in the practice ofthe present invention are, on the one hand, cop per sulfate, notheretofore deemed suitable for use in algicidal granules because of itsrelatively high water solubility, and, on the other hand, compounds suchas CuO, not heretofore deemed suitable because of a relatively low watersolubility. Copper compounds heretofore deemed suitable for use inalgicidal granules be' cause of a rather limited water solubility,particularly under the acidic conditions normally encountered in roofingapplications, are also suitable copper algicidal compounds for use inthe present invention. Cu O and Cu Br are illustrative examples of suchcopper algicidal compounds. As previously indicated, the solubility inwater per se of such algicidal compounds under conditions unrelated tothose encountered in the atmospheric weathering of roofing surfaces isnot deemed of decisive importance in the practice of the presentinvention. The slow release of algicidal ions from the roofing granulesand the resulting leaching thereof over the roofing surface under theconditions encountered during atmospheric weathering so as to producethe desired toxic effect in retarding the biological growth of algaeand/or fungi is at the essence of the present invention. In thatcontext, metallic algicidal compounds of copper and other metals, notheretofore deemed suitable for use in the preparation of algicidalroofing granules, may be employed in the practice of the presentinvention, enhancing the flexibility permissible in the practice of thepresent invention. Illustrative, however, of other copper materials thatcan be used within the scope of the present invention are copperchloride as well as copper metal powders.

The zinc algicidal employed in the practice of the present inventionwill, of course, be any suitable zinccontaining material thateffectively releases zinc ions upon atmospheric weathering underconditions of rain or dew so that such zinc ions are leached from theroofing granules for effectve algicidal action over the entire roofingsurface containing such granules. The most generally preferred zincalgicide from an overall commercial viewpoint is zinc oxide. Otherzinc-containing materials, such as ZnS and metallic oxide pellets orparticles, can also be employed in the practice of the presentinvention.

The simple, economical and effective algicidal action obtained in thehighly flexible embodiments of the present invention are achieved byemploying metallic algicidal materials in amounts generally knownheretofore as being required for effective algicidal control purposes.As the algicides are in a generally more readily accessible form in theroofing granules of the present invention than when incorporated in thecolor coating, the algicidal content of the subject granules can besomewhat less than heretofore employed in conventional algicidal roofinggranules. Thus, zinc algicides may be employed in amounts of from about0.5% by weight up to the amount that can be loaded on the granules,preferably from about 0.75% to about 1% or more by weight based on theweight of base mineral granules employed. Copper algicides can beemployed in amounts generally from about 0.1% to about 1%, preferably atleast about 0.5%, by weight based on the weight of base mineralgranules, Cadmium, silver and nickel-containing compounds, such as theoxides thereof, are effective generally in amounts of from about 0.2% toabout 1%, preferably at least about 0.5%, by weight based on the weightof base mineral granules. A further overall advantage may be obtained byincorporating both copperalgicides and zinc algicides in the posttreatment operation of the invention, in relatively small amounts,ranging from about 0.05% to about 0.5% by weight based on the weight ofbase mineral granules. More particularly, the zinc and copper algicidalmaterials can both be generally employed to advantage in amounts withinthe range of from about 0.l% to about 0.4% by weight based on the weightof base mineral granules. Zinc algicidal contents of from about 0.15% toabout 0.25% by weight based on the weight of base granules have beenfound useful and particularly convenient in particular applications ofthe invention. A particularly convenient copper algicidal content inthis embodiment of the invention is in the range of from about 0.25% toabout 0.35% by weight of base granules. in this embodiment of theinvention, the incorporation of a zinc algicide in amounts veryappreciably below that required for effective algicidal action usingzinc alone, when employed in combination with a relatively small copperalgicidal content, produces a bimetallic toxic effect inhibiting orpreventing the growth of algae and/or fungi. This toxic effect issignificantly more effective than that achieved by employing the copperalgicidal material alone in an amount equal to the total amount of zincand copper algicidal materials employed in this embodiment of theinvention.

The metallic algicidal materials employed in the practice of the presentinvention will have a particle size not exceeding about 100 mesh, withalgicidal materials having a particle size of less than about 200 mesh.More preferably, the algicidal materials employed will be generallyminus 325 mesh. it will be understood in the art that the algicidalmaterials employed will not ordinarily be of uniform particle size butwill have a particle size range. In the more preferred embodiment of theinvention, therefore, the algicidal material will ordinarily have such aparticle size range, the major proportion of the particles, however,being of a particle size smaller than about 325 mesh, i.e. being lessthan 325 mesh. Many convenient, commercially available metallicalgicidal materials are generally available in the art with a particlesize range substantially all of which is minus 325 mesh, e.g. at leastabout 99% minus 325 mesh. Cuprous oxide is a commercial productavailable, for example, with a maximum residue on a 325 mesh screen of0.5% by weight. It is also within the scope of the present invention toemploy metallic algicidal materials having a particle size, or moreprecisely a particle size range, including considerably finer material,generally with the particle size extending from about 44 microns down toabout 20 microns.

Following the post treatment operation of the present invention in whichcolor coated roofing granules, a processing oil composition, andmetallic algicides are mixed, the metallic algicides are found to adhereto the surface of the granule coating. It will be understood, inaddition, that a portion of the metallic algicidal materials,particularly a very fine particle size, will be adsorbed into the colorcoating of the base mineral granules. The presence of the absorption oilis believed to assist in the adherence of the metallic algicides to theroofing granules during subsequent transport, storage and handling bothprior to and after the incorporation of the thus post treated roofinggranules into asphaltic roofing. compositions and the installation ofsuch roofing compositions in household and other commercial roofingapplications. As previously indicated, the processing oil thereafterbreaks down upon exposure to atmopheric weathering conditions within arelatively short period of time, generally in a matter of a few months.The metallic algicides nevertheless, and somewhat surprisingly, arefound to remain on the roofing granule surface and in the roofinggranule color coating and are not eroded away mechanically by wind andrain upon continued exposure to atmospheric weathering. In thusremaining on the roofing granules, the metallic algicidal materialsprovided a source of algicidal ions that are toxic to algae and/or fungiinfestation and bio logical growth. Upon exposure during periods of rainand dew over extended periods of time in roofing serivce, the metallicalgicidal materials become ionized and slowly release metallic algicidalions that are thereupon leached over the surface of the roof to providethe desired retarding effect on the biological growth of algae and/orfungi. The finer sized metallic algicidal materials that are adsorbedinto the moisture permeable, water insoluble color coating appear toserve to provide a reservoir source of algicidal ions further assuringthe continuation of the algicidal properties of the subject roofinggranules over extended periods of time. in addition, the metallicalgicidal materials on that portion of the subject roofing granules thatis embedded in the asphalt coating of the roofing shingle or otherroofing composition are retained over such extended periods of roofingapplication to a greater extent than the metallic algicidal materials onthat portion of the roofing granule that is not embedded in the asphaltcoating. With respect to the metallic algicidal materials embedded inthe asphalt coating, such algicidal materials tend to migrate from theroofing granule-asphaltic coating interface, either with lighterasphaltic oils or otherwise, so as to thereafter become an availablesource of desired algicidal ions to continue the highly desirablealgicidal efi'ect of the subject roofing granules over the reasonablelife of the roofing composition. As a further enhancement over theoverall algicidal effect achieved in the practice of the pres entinvention, periods of heavy rain, as previously noted, tend not only toproduce a desired "wash-out" effect of algicidal ions from relativelywater soluble algicidal materials over the roofing surface, but also toresult in the simultaneous leaching of algicidal ions from such a sourcematerial into the interstices of the moisture permeable color coatingitself. As a result, the

slow leaching of algicidal ions for continued algae andlor fungiretardation over extended periods of exposure to all atmosphericweathering conditions was encountered in use.

The highly advantageous benefits achieved in the practice of the presentinvention are determined and illustrated in laboratory experiments andfield evalua tions of sample asphaltic roofing panels containingalgicidal roofing granules prepared in accordance with the novel posttreatment of color coated roofing granules herein provided. Such fieldevaluations are carried out in the United States and elsewhere underconditions highly conductive to rapid algae development. Periodicevaluation of such sample panels is made to observe usual comparativeeffects that can be reasonably related to the known performance ofconventional roofing granules in ordinary roofing usage under generallyapplicable weathering conditions. Meaningful results are observablewithin periods of time ranging from about 6 months to 2 years for sometest locations and up to about 3-4 years for other such locations. Forcomparative purposes, the algicidal roofing granules prepared inaccordance with the present invention are compared with one another atvarying metallic algicidal contents and with control granules exposedfor the same period of time under the same set of atmosphericconditions. In these experimental runs, ordinary base mineral granulesare coated with color coating paint slurries that are maintained uniformin composition throughout. The coatings thus contain conventionalamounts of sodium silicate, clay and water, together with TiO pigment toproduce a white roofing granule. Such a suitable coating composition,for exam ple, conditions sodium silicate, clay, water and TiO inrespective proportions constituting 50, 40, 55 and lbs. per ton of basemineral granules with which the paint slurry is mixed. A granule firingtemperature of about 950 F is employed to convert the paint slurrycomposition to a hard, durable, tight, weather resistant, fully waterinsolubilized but moisture permeable granule color coating. The posttreatment of the fired granules with processing oil is carried out in aconventional manner with a suitable processing oil, e.g. anaromaticparaffinic processing oil having a viscosity of 300 SUS (SeyboltUniversal Seconds) at l00 F and having a Clay/Gel analysis in by weightof 83.3% saturants, 16. l% aromatics and 0.6% polar compounds. Theprocessing oil is heated to a temperature of about 200 F to assureadequate spread or coverage of the processing oil on the surface of thegranules being most treated. in the preparation of representativealgicidal roofing granules of the present invention, a metallicalgicide, or combination of algicides, is blended with the processingoil and mixed with the color coated roofing granules to produce colorcoated granules having a thin film of processing oil on the surfacethereof, with a por tion of the processing oil absorbed into the colorcoating itself, with metallic algicides adhering to the surface of thegranule coating. in such algicidal roofing granule preparation, themetallic algicides employed have a particle size, or more accurately aparticle size range, not exceeding about 100 mesh. The commericallyavailable metallic algicides generally advantageous for use in thepresent invention are commonly available in a particle size rangeessentially all of which is minus 325 mesh, e.g. about 99% minus 325mesh material. I]- lustrative samples are prepared by the use ofalgicidally effective amounts of metallic algicides together with aconvenient amount of said processing oil, i.e. about 0.625 gallon ofprocessing oil per ton of granules being post treated. In theapplication of the algicidal roofing granules and the control granulesto asphaltic roofing panels, a typical granule loading of about 35 lbs.of granules per sq. ft. of roofing surface is employed.

The laboratory testing and field evaluations serve to establish thealgicidal effectiveness and the overall commercially significantadvantages obtained in the practice of the present invention. Uponweathering away and decompositiion of the post treatment processing oil,the metallic algicidal materials employed are found to remain adheringto the surface of the granule coating, with a portion of the metallicalgicides being present within the color coating itself. The adherenceof the metallic algicides to the granule surface is not adverselyeffected, therefore, by the weathering away of the processing oil. Overextended periods of exposure to atmospheric weathering, the algicidalroofing granules of the present invention are found to be effective ininhibiting or preventing the growth of algae and/or fungi. Duringperiods of rain and dew, therefore, the metallic algicidal materialsbecome ionized upon exposure to atmospheric moisture, and metallicalgicidal ions are thereby released and leached over the surface of thesample roofing panels. Such ionization and release of metallic algicidalions from the novel algicidal roofing granules of the present invention,however, do not occur at such a rapid rate as to deplete the availablesupply of algicidal ions required for effective algicidal control overthe reasonable life of a roofing composition. The algicidal roofinggranules of the invention, therefore, enhance the resistance of aroofing composition to algae and/or fungi discoloration to acommercially satisfactory extent over a highly desirable extended periodof time.

Representative algicidal granules illustrative of the invention are thusprepared and evaluated using the following metallic algicides andproportions in the post treatment with the oil employed in the practiceof the present invention: 0.5% Cu O, 0.5% Cd metal, 0.5% Ni metal, 0.5%Ag metal, 0.85% ZnO and 0.5% Cu O, all by weight based on the weight ofbase granules. The adherence of the algicides to the color coatedgranules is found to exist over extended periods of time during the testevaluations and is not adversely effected by the weathering away of theprocessing oil with which they are associated in the post treatmentoperation of the invention. Wash-off or fall-off of individual algicidalparticles due to poor adherence to the granules, either in handling orduring atmospheric weathering in use, is not encountered so as tojeopardize the supply of algicidal particles available for the slowrelease of algicidal ions upon exposure to rain and dew during use overextended periods of time.

An enhanced toxic effect in retarding the biological growth of algaeand/or fungi is achieved, in the practice of the present invention, bythe incorporation of both copper and zinc algicides in the posttreatment operation of the present invention. The slow release of bothcopper and zinc ions from the subject algicidal roofing granulesproduces a bimetallic toxic effect that is superior to the resultsobtained by use of the same copper algicide at a dosage level equal orexceeding that employed for the combination of zinc and copperalgicides. It is significant to note that this enhanced toxic effect isachieved by incorporating with the copper algicide, a zinc algicide inamounts ineffective for algicidal control purposes when said zincalgicide is employed alone, particularly when incorporated in thegranule color coating. The combination of zinc and copper algicide beingfound to be particular effective when employed in amounts of at leastabout 01% up to about 0.4%. ZnO and Cu O or a combination of Cu O andcopper sulfate are conveniently employed in the field evaluation studiesas to the effectiveness of the present invention.

The present invention has been herein described principally withreference to the post treatment of conventionally color coated roofinggranules, such as the artificially colored granules employed incommercially available asphaltic roofing compositions. It should benoted, however, that the treatment of roofing granules with processingoil and metallic algicides as herein disclosed and claimed, withreference to the post treatment of colored roofing granules, can also beemployed for the treatment of natural, uncolored base mineral granulesas well. As in the post treatment operating of the present invention,natural base mineral granules can be conveniently treated by mixing suchnatural granules with a suitable amount of processing oil together withcopper silicate and metallic algicides having a particle size and dosagelevel generally the same as that indicated herein with respect to thepost treatment of colored roofing granules. Upon incorporation of suchalgicidal, uncolored mineral granules in asphaltic roofing compositions,the adherence of the algicidal materials will be found to continuesatisfactorily for extended periods of time long after the processingoil has weathered away. During periods of rain and dew, the algicidalmaterials on the natural granule surface will become ionized and slowlyrelease metallic algicidal ions that, as in the case of the algicidalcolored roofing granules, will be slowly leached over the surface of theroof, providing the desired toxic effect in retarding the growth ofalgae and/or fungi. It should also be noted that conventional siliconecoating compositions can be employed together with a suitable processingoil, either in the post treatment of color coated granules or in thetreatment of natural granules as herein suggested, to further enhancethe adherence of the copper silicate and metallic algicides to thesurface of the granules and to further assure against undesiredattrition ofsuch particles during transport, storage and handling priorto the placement of roofing composition incorporating such algicidalgranules in service as a weather resistant roofing covering. It is alsowithin the scope of the in vention to incorporate TiO or other pigmentin the processing oil composition, together with the algicidalmaterials, silicone and the like, for application to either color coatedgranules or to natural granules to provide or enhance a desired granulecoloration.

While the invention has been described herein with reference to the useof a variety of metallic algicides and combinations thereof, it will beunderstood that other metallic algicides presently or hereinafteravailable in the art can be utilized in the novel algicidal granules ofthe invention, produced by the novel post treatment operation hereindisclosed and claimed. Various combinations of metallic algicides canalso be employed within the scope of the invention. As indicated aboveparticularly with respect to copper algicides, the present inventionpermits the use of metallic organic algicides that are generallyunsuited for incorporation in the granule color coating because of theadverse effect of the granule firing temperatures used to insolubilizethe color coating. It should also be noted that the post treatmentoperation as herein described with reference to metallic algicides canalso be employed using non-metallic materials having algicidalproperties, i.e., the ability to slowly release toxic ions or materialsfor leaching over the surface of the roof during periods of rain anddew. While the post treatment operation of the invention has herein beendescribed with reference to the employement of algicidal materials withthe processing oil used in the treatment of natural granules and thepost-treatment of colored granules, with or without additional algicidalmaterials present in the color coat, it should be noted that materialsother than algicides can be employed with said processing oilcomposition. Particularly with reference to natural granules, forexample, the processing oil composition can be used as a carrier for avariety of treating materials such as pesticides. For example, thetreated granules may have water releasable and leachable dog repellentmaterials, herbicides and the like adhering thereto as a result of theirincorporation with the processing oil used to treat such granules, as inthe post treatment of the color coated roofing granules. Upon mixingwith the base mineral granules, the processing oil composition, with orwithout a silicone therein, will form a thin film on the granulesurface, with a portion of said oil being absorbed into the granuleitself. The treating materials carried by the oil will adhere to thesurface of the granule, the finer sized particles of such materialspossibly being absorbed into the granule itself. The particle size ofthe treating materials, if present in solid form, will be as set forthabove with respect to algicidal particles. Liquid algicidal or othertreating materials mixed with the processing oil and with the basemineral granules being treated, either natural or color coated, willlikewise form a film on the surface of the granule, with a portionthereof being absorbed into the granule. Granules thus incorporatingtreating materials other than algicidal materials can be employed in anyconvenient manner appropriate to the functional purpose of the treatingmaterial. Granules thus treated to incorporate dog repellentcompositions or herbicides, for exmaple, can be distributed on theground over the area to be treated. Upon exposure to atmosphericweathering, the processing oil will weather away and decompose, as inconventional post-treated roofing granules. The treating materials willcontinue to adhere to the granules, however, for slow release overextended periods of time during periods of rain or dew, as in the slowrelease of algicidal ions from the roofing granules posttreated inaccordance with the present invention.

It will also be understood that, in determining the commercialsignificance of algicidal roofing granules, a balance must be drawnbetween the desired algicidal control and the cost of the subjectalgicidal roofing granules, in light of pertinent practical marketingconsiderations. Thus, the degree of algae control achieved, thesignificance of such control in terms of the ordinary life of theroofing surface, the esthetic effect of even moderate algae growth,particularly on white or light colored roofs, including the objectivemarketing effect of any unsightly algae and/or fungi discoloration, allin the light of the necessary incremental increase in the price ofroofing compositions to achieve whatever degree of algae control isobtained, are all pertinent factors in determining the commercialsignificance of a novel algicidal roofing granule. The present inventionis found to present a highly advantageous balance of such pertinentfactors, providing a highly effective algae and/or fungi inhibitingeffect at minimal incremental cost as compared with conventional,nonalgicidal roofing granules.

The process of the present invention for the production of algicidalroofing granules is simple, economic, entirely compatible with theoverall requirements of conventional production of color coated roofinggranules, and capable of being carried out with minimum disruption ofsuch conventional production operations. In addition, the process of thepresent invention has an inherent flexibility as to the nature of thealgicidal material employed and the resulting characteristics of thealgicidal control effect that is highly desirable in the art. As theamount of algicidal material employed to achieve effective retardationof the biological growth of algae and/or fungi in the algicidal roofinggranules of the present invention is relatively low, the highlyfavorable processing advantages in the production of such roofinggranules is not offset by an undue incremental cost for the algicidalmaterials employed in the roofing granules of the present invention. Theincremental cost for TiO; or other conventional pigment content of thecolor coating to offset any undesired color effect resulting from theuse of algicidal materials is also relatively small and economicallyacceptable. From an overall economic viewpoint, therefore, the presentinvention permits the availability in the art of algicidal roofinggranules at a minimal incremental cost unobtainable by any previouslyconsidered techniques for imparting algicidal properties to roofinggranules.

The highly advantageous production and overall economic advantagesobtainable in the practice of the present invention are accompanied by ahighly effective performance by the subject algicidal roofing granulesin providing a supply of metallic algicidal ions for leaching over thesurface of roofing compositions containing such granules to retard orprevent the infestation and growth of algae and/or fungi. The highdegree of effective algae control obtainable by means of the algicidalroofing granules of the present invention, furthermore, is found topersist upon atmospheric exposure of roofing compositions containingsuch granules over extended periods of time consistent with thereasonable life of the roofing composition itself. Thus, the roofingcomposition is provided with an enhanced resistance to unsightlydiscoloration during such extended periods of exposure to atmosphericweathering particularly in humid environments conducive to the growth ofalgae and fungi. The present invention, therefore, is of significance tothe roofing industry, providing a highly effective, but practical andeconomically favorable solution to the problem of algae and/or fungidiscoloration of roofing surfaces. The algicidal roofing granules of thepresent invention and roofing compositions containing such granulesrepresent, in ef feet. a high quality, premium product at minimal economic cost and optimum suitability for ready incorporation in standardcommercial operations in the roofing industry.

Therefore, I claim:

I. Algicidal roofing granules capable of inhibiting or preventing thegrowth of discoloring algae and fungi organisms upon exposure of roofingsurfaces containing such granules to atmospheric weathering for extendedperiods of time, comprising:

a. base mineral granules;

b. a moisture permeable, durable, water insolubilized, pigmented, fired,inorganic alkali metal silicateclay coating on said base granules;

c. a processing oil composition present in an amount within the range offrom about one-fourth gallon to about 1% gallons per ton of basegranules, said processing oil forming a thin film on the surface of saidcoated granules, said processing oil having a viscosity within the rangeoffrom about to about 500 SUS, measured at 100 F; and

d. metallic algicides in the oil film and adhering to the surface ofsaid granule coating, said algicides having a particle size notexceeding about 100 mesh and being present in amounts within the rangeof from about 0.05% to about 1.0% by weight based on the weight of thebase mineral granules, metallic algicidal ions being leachable from saidalgicides upon exposure thereof to moisture during atmosphericweathering, whereby the weathering away of said processing oil uponstmospheric exposure of rooting surfaces incorporating said granulesdoes not adversely affect the adherence of said metallic algicides tosaid granule coating, the presence of moisture during periods of rainand dew causing ionization of said metallic algicides with the resultingmetallic ions being slowly leached from said granules to retard thegrowth of algae and fungi, thus enhancing the resistance of said roofingsurfaces containing such granules to discoloration during extendedperiods of exposure of atmospheric weathering.

2. The algicidal roofing granules of claim 1 which said algicides have aparticle size of less than about 200 mesh.

3. The algicidal roofing granules of claim 2 in which said algicideshave a particle size the major proportion of which is less than 325mesh.

4. The algicidal roofing granules of claim 3 in which a portion of saidprocessing oil is absorbed into the coating on said base granules, saidprocessing oil composition containing a silicone composition in anamount within the range of from about 1% to about 25% by weight based onthe total weight of said processing oil composition.

5. The algicidal roofing granules of claim 4 in which a portion of saidprocessing oil is absorbed into said base granules.

6. The algicidal roofing granules of claim 4 in which said algicideshave a particle size at least about 99% of which is minus 325 mesh.

7. The algicidal roofing granules of claim 6 in which said metallicalgicides have a particle size generally within the range of from about44 microns to about 20 microns.

8. The algicidal roofing granules of claim 4 in which said processingoil is present in an amount within the range of from about one-half toabout three-fourth gallon per ton of base mineral granules.

9. The algicidal roofing granules of claim 8 in which about 0.625 gallonof processing oil is present per ton of said base mineral granules.

10. The algicidal roofing granules of claim 4 in which said processingoil has a viscosity of from about 100 to about 300 SUS.

11. The algicidal roofing granules of claim 4 in which said processingoil has a viscosity of from about 300 to about 500 SUS.

12. The algicidal roofing granules of claim 4 in which said metallicalgicide comprises a cadmium algicide.

13. The algicidal roofing granules of claim 4 in which said metallicalgicide comprises a nickel algicide.

14. The algicidal roofing granules of claim 4 in which said metallicalgicide comprises a silver algicide.

15. The algicidal roofing granules of claim 4 in which said metallicalgicide comprises a copper algicide.

16. The algicidal roofing granules of claim 4 in which said algicidecomprises a zinc algicide.

17. The algicidal roofing granules of claim 4 in which said metallicalgicide comprises a mixture of copper and zinc algicides.

18. The algicidal roofing granules of claim in which said copperalgicide comprises Cu O.

19. The algicidal roofing granules of claim 15 in which said copperalgicide comprises copper sulfate.

20. The algicidal roofing granules of claim 16 in which said zincalgicide comprises ZnO.

21. The algicidal roofing granules of claim 17 in which said zincalgicide comprises ZnO and said copper algicide comprises Cu O.

22. The algicidal roofing granules of claim 17 in which said zincalgicide comprises ZnO and said copper algicide comprises a mixture ofCu O and copper sulfate.

23. The algicidal roofing granules of claim 15 in which said copperalgicide is present in an amount within the range of from about 0.1% toabout 1.0% by weight based on the total weight of said base granules.

24. The algicide roofing granules of claim 16 in which said zincalgicide is present in an amount of at least about 0.75% by weight basedon the weight of said base granules.

25. The algicidal roofing granules of claim 17 in which said copper andzinc algicides are both present in an amount within the range of fromabout 0.05% to about 0.5% by weight based on the total weight of saidbase granules.

26. The algicidal roofing granules of claim 18 in which said Cu O ispresent in an amount within the range of from about 0.1% to about 0.4%by weight based on the total weight of said base granules.

27. The algicidal roofing granules of claim 20 in which said ZnO ispresent in an amount within the range of from about 0.l% to about 0.4%by weight based on the total weight of said base granules.

28. The algicidal roofing granules of claim 6 in which a portion of saidmetallic algicides is absorbed into the silicate-clay coating on saidbase mineral granules.

29. The algicidal roofing granules of claim 25 in which at least themajor proportion of said metallic algicides has a particle size of lessthan about 325 mesh, a portion of said metallic algicides being absorbedinto the silicate-clay coating on said base mineral granules.

30. The algicidal roofing granules of claim 29 in which said metallicalgicides have a particle size at least about 99% of which is minus 325mesh.

1. ALGICIDAL ROOFING GRANULES CAPABLE OF INHIBITING OT PREVENTING THEGROWTH OF DISCOLORING ALGAE AND FUNGI ORGANISMS UPON EXPOSURE OF ROOFINGSURFACES CONTAINING SUCH GRANULES TO ATMOSPHERIC WEATHERING FOR EXTENDEDPERIODS OF TIME, COMPRISING A. BASE MINERAL GRANULES, B. A MOISTUREPERMEABLE, DURABLE, WATER INSOLUBILIZED, PIGMENTED, FIRED, INORGANICALKALI METAL SILICATECLAY COATING ON SAID BASE GRANULES, C. A PROCESSINGOIL COMPOSITION PRESENT IN AN AMOUNT WITHIN THE RANGE OF FROM ABOUTONE-FOURTH GALLON TO ABOUT 1 1/2 GALLONS PER TON OF BASE GRANULES, SAIDPROCESSING OIL FORMING A THIN FILM ON THE SURFACE OF SAID COATEDGRANULES, SAID PROCESSING OIL HAVING A VISCOSITY WITHIN THE RANGE OFFROM ABOUT 100 TO ABOUT 500 SUS, MEASURED AT 100*F, AND D. METALLICALGICIDES IN THE OIL FILM AND ADHERING TO THE SURFACE OF SAID GRANYLECOATING, SAID ALGICIDES HAVING A PARTICLE SIZE NOT EXCEEDING ABOUT 100MESH AND BEING PRESENT IN AMOUNTS WITHIN THE RANGE OF FROM ABOUT 0.05%TO ABOUT 1.0% BY WEIGHT BASED ON THE WEIGHT OF THE BASE MINERALGRANULES, METALLIC ALGICIDAL IONS BEING LEACHABLE FROM SAID ALGICIDESUPON EXPOSURE THEREOF TO MOISTURE DURING ATMOSPHERIC WEATHERING, WHEREBYTHE WEATHERING AWAY OF SAID PROCESSING OIL UPON STMOSPHERIC EXPOSURE OFROOFING SURFACES INCORPORATING SAID GRANULES DOES NOT ADVERSELY AFFECTTHE ADHERENCE OF SAID METALLIC ALIGICIDES TO SAID GRANULE COATING, THEPRESENCE OF MOISTURE DURING PERIODS OF RAIN AND DEW CAUSING IONIZATIONOF SAID METALLIC ALIGICIDES WITH THE RESULTING METALLIC IONS BEINGSLOWLY LEACHED FROM SAID GRANULES TO RETARD THE GROWTH OF ALGAE ANDFUNGI, THUS ENHANCHING THE RESISTANCE OF SAID ROOFING SURFACE CONTININGSUCH GRANULES TO DISCOLORATION DURING EXTENDED PERIODS OF EXPOSURE OFATMOSPHERIC WEATHERING.
 2. The algicidal roofing granules of claim 1which said algicides have a particle size of less than about 200 mesh.3. The algicidal roofing granules of claim 2 in which said algicideshave a particle size the major proportion of which is less than 325mesh.
 4. The algicidal roofing granules of claim 3 in which a portion ofsaid processing oil is absorbed into the coating on said base granules,said processing oil composition containing a silicone composition in anamount within the range of from about 1% to about 25% by weight based onthe total weight of said processing oil composition.
 5. The algicidalroofing granules of claim 4 in which a portion of said processing oil isabsorbed into said base granules.
 6. The algicidal roofing granules ofclaim 4 in which said algicides have a particle size at least about 99%of which is minus 325 mesh.
 7. The algicidal roofing granules of claim 6in which said metallic algicides have a particle size generally withinthe range of from about 44 microns to about 20 microns.
 8. The algicidalroofing granules of claim 4 in which said processing oil is present inan amount within the range of from about one-half to about three-fourthgallon per ton of base mineral granules.
 9. The algicidal roofinggranules of claim 8 in which about 0.625 gallon of processing oil ispresent per ton of said base mineral granules.
 10. The algicidal roofinggranules of claim 4 in which said processing oil has a viscosity of fromabout 100 to about 300 SUS.
 11. The algicidal roofing granules of claim4 in which said processing oil has a viscosity of from about 300 toabout 500 SUS.
 12. The algicidal roofing granules of claim 4 in whichsaid metallic algicide comprises a cadmium algicide.
 13. The algicidalroofing granules of claim 4 in which said metallic algicide comprises anickel algicide.
 14. The algicidal roofing granules of claim 4 in whichsaid metallic algicide comprises a silver algicide.
 15. The algicidalroofing granules of claim 4 in which said metallic algicide comprises acopper algicide.
 16. The algicidal roofing granules of claim 4 in whichsaid algicide comprises a zinc algicide.
 17. The algicidal roofinggranules of claim 4 in which said metallic algicide comprises a mixtureof copper and zinc algicides.
 18. The algicidal roofing granules ofclaim 15 in which said copper algicide comprises Cu2O.
 19. The algicidalroofing granules of claim 15 in which said copper algicide comprisescopper sulfate.
 20. The algicidal roofing granules of claim 16 in whichsaid zinc algicide comprises ZnO.
 21. The algicidal roofing granules ofclaim 17 in which said zinc algicide comprises ZnO and said copperalgicide comprises Cu2O.
 22. The algicidal roofing granules of claim 17in which said zinc algicide comprises ZnO and said copper algicidecomprises a mixture of Cu2O and copper sulfate.
 23. The algicidalroofing granules of claim 15 in which said copper algicide is present inan amount within the range of from about 0.1% to about 1.0% by weightbased on the total weight of said base granules.
 24. The algicideroofing granules of claim 16 in which said zinc algicide is present inan amount of at least about 0.75% by weight based on the weight of saidbase granules.
 25. The algiCidal roofing granules of claim 17 in whichsaid copper and zinc algicides are both present in an amount within therange of from about 0.05% to about 0.5% by weight based on the totalweight of said base granules.
 26. The algicidal roofing granules ofclaim 18 in which said Cu2O is present in an amount within the range offrom about 0.1% to about 0.4% by weight based on the total weight ofsaid base granules.
 27. The algicidal roofing granules of claim 20 inwhich said ZnO is present in an amount within the range of from about0.1% to about 0.4% by weight based on the total weight of said basegranules.
 28. The algicidal roofing granules of claim 6 in which aportion of said metallic algicides is absorbed into the silicate-claycoating on said base mineral granules.
 29. The algicidal roofinggranules of claim 25 in which at least the major proportion of saidmetallic algicides has a particle size of less than about 325 mesh, aportion of said metallic algicides being absorbed into the silicate-claycoating on said base mineral granules.
 30. The algicidal roofinggranules of claim 29 in which said metallic algicides have a particlesize at least about 99% of which is minus 325 mesh.